where \(R_S\)  is the solar neutrino rate in the energy interval \(\Delta E\)  and \(\sigma (R_{tot})\)  is the width of the distribution of the total rate \(R_{tot}\)  in said energy range. The chosen energy RoI is 150-428 Npe, corresponding to 300-827 keV, is highlighted in yellow in Fig. REF .
The mono-energetic peak of quenched \(^{210}\) Po alpha events
is drastically reduced via high efficiency pulse shape discrimination based on multi-layer perceptron (MLP) [1]}, [2]}. What is left in the energy RoI is mostly from the mono-energetic \(^{7}\) Be solar neutrinos, whose electron scattering is characterized by a typical Compton-like shoulder, and a subdominant contribution from \(pep\)  and CNO neutrinos. Backgrounds contributing to this region include: \(^{210}\) Bi and \(^{85}\) Kr \(\beta \)  decays, a small \(\gamma \) -ray contribution from \(^{40}\) K, \(^{214}\) Bi, \(^{208}\) Tl external to the fiducial volume, and cosmogenic \(^{11}\) C \(\beta ^+\)  decays. The Borexino \(\beta \) -like spectrum is reported in full detail in Ref. [3]}.
